DISEASE AND RELATED PHENOMENA IN ANIMAL BREEDING 533 
that in crossbreeding, namely of keeping pure-bred herds of both zebu 
and Northern cattle and continually crossing them. Central herds of 
zebus could easily be established to supply the demand for zebu bulls. 
Zebu bulls appear to be more prolific than Northern bulls, for it is possible 
with them to count upon an average of about sixty calves per year from 
each bull. The utilization of the hybrids for the establishment of a new 
breed is another matter, and one requiring long time and careful attention. 
It should, however, be carried on under competent guidance such as 
might be afforded by experiment station supervision. 
Fie. 207.—Bison bull, Bison americanus. (Courtesy National Zoological Park, Wash- 
ington, D. C.) 
The other hybrid which gives some promise of use in American 
agriculture is that obtained by crossing the bison and domestic cattle. 
Reciprocal hybrids may be obtained, but apparently it is easier to get 
hybrids by using a bison bull on domestic cows. This hybrid represents 
a more violent cross than the zebu hybrid, inasmuch as considerable 
difficulty attends the production of hybrid progeny. Cows very often 
die while calving, apparently on account of the physical difficulties 
involved in giving birth to the hybrids, which possess a considerable 
hump like that on the bison. The hybrids are intermediate between the 
parents in respect to most characters. In vigor and size they are su- 
perior to either parent; from the market standpoint both with respect 
to flesh and coat they are very desirable animals. Practically all the 
animals which have been born have been females, and these are fertile. A 
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